London Mil
The point I am trying to make is that the more variables there are the easier it is for someone to get it wrong.
I am quite sure that professionals like yourself don't consider it a problem. This is fine. But as you have said "juggling with pressure settings".
Why should "juggling" be necessary? If all a/c in a particular ASR are on the same setting (QNH) whether in transit or circuit, everyone knows where everyone else is.
In a situation :- a/f elevation 500ft a/c approaching circuit on QFE at 2000ft, a/c in transit reports alt 2500 QNH, a conflict exists but may not be realised. Why make life difficult? Transition alts & levels are a different issue & based on QNH or 1013.2 anyway, & QFE if high enough could bust them.
What I am saying is, we can all do the sums, we know metres are bigger than feet so we don't need so many of them, but why should we sit there doing sums desperately in order to stay alive?
In fact 1013.2 is a prime example of standardising pressure settings over a large area, terrain not being such a problem.